The present invention relates generally to gas appliances and, more particularly, to controls for gas input to gas appliances.
Gas appliances typically include valves for controlling gas input to the appliance""s burners. Gas control valves are used in induced draft systems and in forced draft systems with pressure-assist modulation (PAM) to deliver gas to be combined with air for combustion. It is desirable to control gas and air input pressures in order to achieve desired combustion rates in appliance burners. One method of controlling gas input pressure is to electronically modulate gas control valve output relative to the air input pressure, by using a pressure transducer. Such an approach, however, is expensive.
The present invention in one embodiment is an improved gas appliance having a burner, a gas valve through which the flow of combustion gas to the burner is controlled, and a motor driven blower that supplies combustion air to the burner. The improvement includes means for increasing the flow of gas through the gas valve as the blower speed increases, and decreasing the flow of gas through the gas valve as the blower speed decreases, based on a pressure signal generated independently of the combustion air pressure. In a preferred embodiment, a pump provided on the shaft of the blower motor is driven by the blower motor to generate the pressure signal for controlling the gas valve.
The above-described system allows a constant ratio of gas to air to be maintained to the burner while a combustion flow rate varies dependent on the blower motor revolutions per minute. Thus input pressures to the burner can be simply and reliably controlled at low cost.